1. The Field of the Invention
The invention generally relates to the field of optical transmitters. More specifically, the invention relates to optical transmitters packaged with integrated diodes.
2. Description of the Related Art
Modern day computer networks allow for transmissions of large amounts of data between computer terminals. Data may be transmitted on a network across a number of different mediums. For example, data may be transmitted across traditional copper wire based cables. However, copper wire based cables are subject to limitations that are making them less attractive as a solution for many modern networks. Specifically, the copper wire based cables are limited in the amount of data they can carry in a given time period and the length that the data can travel. As computer technology continues to increase in the amount of data that can be produced in a given time period, other types of cable with higher capacities and longer transmission distances may be desirable.
One type of cable that is capable of higher data transmission rates over longer distances is fiber-optic cable. Fiber-optic cables are plastic or stretched glass cables that carry data signals in the form of light. Light signals can propagate on fiber-optic cables at higher speeds and for longer distances than electronic signals on copper wire based cables. Further, fiber-optic cables are potentially lighter weight and less expensive that their copper based counterparts. Thus, fiber-optic cables are steadily becoming a more popular choice for communication networks.
While fiber-optic data signal are optical or light signals, data signals at computer terminals generally continue to be electronic data signals. The electronic data signals being sent by a computer terminal are therefore converted using an electro-optical transducer, such as a laser diode or light emitting diode (LED) that converts the electronic data signals to corresponding optical data signals. To receive a signal from a fiber-optic network, a computer terminal converts the optical data signal to a corresponding electronic signal using an opto-electronic transducer, such as a photodiode and post-amplifier.
A laser diode emits laser light at varying power levels when a varying power level electronic signal is applied to anode and cathode terminals of the laser diode. Thus a modulated optical signal can be produced directly from a corresponding modulated electronic data signal using a laser diode. There is however, often a need to control or monitor the actual power being output by a laser diode or LED. Digital optical signals are often required to be within a certain power level. Thus, there may be a need to measure the amount of power being output by a laser diode or LED and to control that power. It may also be beneficial to monitor the output power of a laser diode or LED to ensure that the laser diode or LED is functioning. Still other reasons may exist for monitoring laser diode and LED power.
Accordingly, some discrete optical sources such as laser diodes and LEDs are packaged with discrete back monitor photodiodes. A back monitor photodiode measures optical power transmitted in a path in which the back monitor photodiode lies (e.g. the output of a laser diode or LED). Alternatively, a back monitor photodiode may measure optical power that is reflected off of the packaging or other external reflection causing elements. Thus the back monitor photodiode receives a small portion of the actual power that is generated. The amount of power detected by the back monitor photodiode is then scaled to approximate the amount of power produced by the optical source.
Unfortunately, current designs suffer from several drawbacks. For example, the use of discrete components results in inconsistencies in how the back monitor photodiode receives optical power. Further, packaging and/or other external elements that reflect light are typically not configured to reflect light into a back monitor photodiode. Thus, any power reflected back into the back monitor photodiode is not regulated or controlled and in some environments is at least partially random. Additionally, the small size of the back monitor photodiode represents a reduced area for incident reflected power.
What would be useful therefore is a back monitor photodiode with a substantial surface area. Further it would be useful to incorporate a package that directed more reflected power into the back monitor photodiode. Further still, it would be useful if the cost of the optical source and back monitor photodiode can be reduced.
Another challenge that is experienced in laser devices such as Vertical Cavity Surface Emitting Lasers (VCSELs) relates to Electrostatic Discharge (ESD) damage. Exposure to ESDs is one very common cause of VCSEL failure. Further, the smaller an aperture of emission in the VCSEL, the lower the amount of ESD voltage a VCSEL can withstand. As an example, a VCSEL with a aperture diameter of about 5 microns may be damaged when ESD levels are on the order of about 100V using a human ESD model. Smaller apertures are often used in single mode VCSELs. Thus single mode VCSELs may be more susceptible to ESDs than other types of VCSELs
To protect devices from electrostatic discharge, external components may be used to limit the amount of current through a component or to provide an alternate path for the discharge. However, using external components significantly increases the total size of packaging needed. This may be less desirable when there is a need or advantage to having smaller component packaging. Therefore, what would be new and useful is electrostatic discharge protection that can be implemented without significantly increasing the size of components.